Teebitoey



0. HOFMANN.

ORE FURNACE.

Patented Sept. '20, 1881. v

w N. PETERS. Phulu-Llhogmphen Washmglon. n, c

v IUNITED STATES PATENT OF ICE.

ORE-FURNACE.

SPECIFICATION forming part of Letterslatent No. 247,193, dated September 20,1881,

Application filed June 27, 1881. (N omo(1el.)

To all'whom it may concern:

Be it known that I, OTTOKAR HOFMANN, of the town and county of Final, Territory of Arizona, have invented an Improved Revolving Ore-Roasting Furnace and I hereby declare the following to be a full, clear, and exact description thereof.

My invention relates to certain improvements in revolving ore-roastin g furnaces; and it consists in combining with a revolving cylinder-furnace two fire-places, one at each end, and connecting both with the furnace, and also with an escape-flue. Suitable dampers are fitted between each fire-place and the escape=flue, so that when a fire is built in one fire-place its damper may be closed and the flame directed through the furnace, and thence through the opposite fire-placeand its flue to the chimney. After the ore at the end of the cylinder nearest thefirst fire-place is properly roasted and chloridized a fire is built in the other fire-place and the first one suffered to godown. Thedamperofthefirstoneisopened, while that of the second one is closed, so that the direction of the heat is changed, and the ore nearest this second fire is subjected to the highest temperature. This enables me to roast and chloridize the ore quickly without exposing that at one end to an injurious temperature in order to heat that at'the opposite end to a sufficient temperature.

Referring to the accompanying drawing for a more complete explanation of my invention, the figure is a view of the cylinder with a longitudinal section of the fire-places and flues.

The revolving roasting-furnace as ordinarily constructed consists of an iron cylinder, lined on the inside with bricks, and provided on one end with a fire-place, and on the other with a flue leading to the chimney. The shape of some of these revolving furnaces is prismatic; but in construction they do not difi'er materially from the cylinder-furnace. There are on the mantle of the cylinder four doors for charging and discharging. After the furnace is charged with ore and the doors are closed the cylinder is set into a slow revolving motion, while the flames and gases pass in the direction from the fire-place to the flue, and through it into the chimney.

It is apparent that that part of the ore which is nearest to the fire will be exposed to ahigher temperature than that on the farther end and as the ore, by the revolving motion of the furnace, is mixed and turned, but does not change its respective place in the furnace, it is further apparent that no uniform roasting can be obtained, at-least not without causing an'unnecessary loss of silver by volatilization.

I have found that part of the ore whichis nearest to the fire perfectly roasted and chloridized, while the ore at the other end has been from five to ten and more per cent. less chloridized. In order to bring the chlorination up,

the temperature had to be increased and roast-- ing continued for considerable time'longer, which increased and continued heat disposes silver to volatilize. The same ore will lose less silver if the ohloridizing roasting is completed in a short time than it will in a longer period, and, again, will lose less if the chloridizing roasting is performed at a lower heat; but as these revolving furnaces are constructed, (especially if long cylinders are used-say sixteen feet long,) the metallurgist encounters great difficulties to treat the charge of ore in the furnace to the best advantage, and is not able to obtain nearly satisfactory results it it contains a great deal of antimony, and bakes easily, as the construction of the furnace does not give him the facilities to subject the ore to a uniform heat. 1

Antimonious ores have to be roasted at a verylow heat; but if the fire is kept low enough for the ore nearest to it, the ore on the fartheroff part of thefurnace willnothaveheat enough to roast; and, again, if the fire is kept strong enough for the farther part,the ore nearest to the fire will commence to cake and sustain a heavy loss in silver.

To avoid these difficulties, and to enable the roaster to roast his ore uniform at the temper ature it requires, 1 made the following improvement in the construction of the revolving roasting-furn aces Opposite to the fire-place, and on the end of the cylinder where in the old construction the line is, I erect a second fire-place, so that the furnace A is provided with two fire places, b and c, on each end one. Each fire-place is provided with a flue and damper, d and a, leading to the main line 6 and chimney. By

ICO

attaching the flue directly to the fire-place I can make, by shutting the ash -pit and firedoor and raising the damper in the flue, the fire-box serve alternately as fire-place or flue, according which way the flame is directed.

In working the furnace the operations are as follows: After the furnace is charged with ore the fire is built in the fire-place c and the damper a closed. The flame and gases traverse the furnace A and pass through the opposite fire-place, b, and the flue into the main flue 0. After a lapse of an hour fire is built in the opposite fire-place, b, the damper wopened, and (1 closed. Flame and gases are now forced to pass through the furnace in the opposite direction. This changing of the fire is kept up in hourly intervals during the whole time of roasting. While one fire is in operation the other is allowed to go down.

With this double fire-place and flue arrangement I am able to subject the ore from both halves of the furnace to the required roasting temperature, thus obtaining a uniform roasting throughout the whole furnace without the disadvantage of burning one-half too much in order to throw enough heat on the other. Furthermore, it enables me to treat certain classes of ore which bake easily successfully in this furnace. Besides this my improvement enables me to prevent the dust from being carried by the draft into the flue during the charging of the furnace.

In charging ordinary furnaces the doorsf and g are opened and placed under the outlets of a hopper. The ore falls in a shower into the furnace, and the draft passing through the furnace carries ofi' considerable valuable dust into the flue. To avoid this I open during the time of charging both dampers d and a. The draft now passes through each fire-place and flue into the main flue independent of the furnace, through which no draft at allis passing.

This prevents the loss above mentioned.

Having thus described my invention, what I claim as new, and desire to secure by Letters Patent, is

l. The improvement in revolving cylinder and prismatic-shaped roasting furnaces consisting of the fire-places b c at each end of the revolving furnace A, each fire-place having a flue leading to the main flue or dust-chamber and controlling-dampers a d, substantially as and for the purpose herein described.

2. The combination of the fire-places c b and flues having dampers a d with the furnace A, the flues being attached to the firebox, thus communicating the same directly with the main flue, or through the furnace and the opposite firebox to the flue, substantially as and for the purpose herein described.

In witness whereof I have hereunto set my hand.

OTTOKAR HOFMANN. Witnesses:

GUSTAVUS 00X, CHAS. V. BESELER. 

